The present invention relates to a high voltage power switch having an axially displaceable contact and utilizing compressed gas and an electromagnetic field to distinguish arcs formed upon opening of the contacts.
A switch of this type is generally disclosed in European Patent Application No. 0,004,213. In the contact opening operation of this switch, the pressure of the gas present in a compression chamber is increased as the result of heating by the electric arc formed between the contacts. The arc is rotated by a radial magnetic field, and blown by the heated pressurized gas to extinguish it. In order to obtain a high contact disconnect capacity in a switch of this type, it is necessary that the coil connected to the hollow stationary contact be large enough so that it is capable of absorbing the entire quenching current. However, an adequately dimensioned coil will substantially increase the cost of the switch. Furthermore, the quenching capacity of the switch is not optimal even when using large coils, because the heat generated by the electric arc cannot be removed rapidly enough from inside the switch.
It is therefore the general object of the present invention to provide a novel switch wherein the contact disconnect capacity is increased by means of an improved exchange of gas between the arc and the surrounding pressurized gas, and wherein the coil connected with the hollow commutating contact has small dimensions.
This and other objects and advantages are obtained according to the present invention by configuring the stationary commutating contact as a nozzle, and using the compressed gas to commutate the arc from a first part to a second part of the stationary commutating contact during a half-wave of the extinguishing current. The switch according to the invention is advantageous in that only a slight quenching current flows through the coil connected with the stationary commutating contact only shortly before the current flow stops as it changes from one polarity to the other. The oil therefore has relatively small dimensions. In addition, the commutating contact is designed so that a magnetic field extending in the axial direction acts on a large part of the arc. The forces generated by the axial magnetic field pump energy into the random, tuburlent motion of gas and produce a particularly strong breaking of the arc in the expansion chamber, thus resulting in a high extinguishing capacity of the switch.
In one particular embodiment, the nozzle portion of the commutating contact forms a shading ring. Thus, the magnetic field of the coil is limited, by the shading ring, to the expansion chamber of the switch. By means of material recesses provided in the commutating contact, the axial magnetic field may be confined in a particularly appropriate manner inside the contact.
Furthermore, by providing a piston in the annular space between the commutating contact and a gas flow directing nozzle, the commutation of the arc from the first to the second part of the commutating contact is obtained safely by the use of simple means, even in the case of very low currents.
Further advantages and features of the invention will be appreciated upon a perusal of the followed detailed description of a preferred embodiment of the invention.